A fiber laser apparatus is known as one of laser apparatuses. The fiber laser apparatus includes an amplifier optical fiber doped with a rare earth element. Laser light is amplified by this amplifier optical fiber, such that the amplified laser light is output from an end of the amplifier optical fiber.
In such a fiber laser apparatus, the power intensity of laser light is high at the end of the amplifier optical fiber. For this reason, damage may be caused at the end of the amplifier optical fiber. To prevent such damage, a fiber laser apparatus is known which is configured to output laser light with power intensity reduced at the output end. The following Patent Document 1 describes such a fiber laser apparatus. In the fiber laser apparatus described in Patent Document 1, a first endface of a glass rod is connected by fusing to an endface of an amplifier optical fiber, the diameter of the glass rod being larger than the diameter of the core of the amplifier optical fiber. The laser light amplified by the amplifier optical fiber is input to the glass rod from the amplifier optical fiber. The diameter of the laser light that has been input to the glass rod is spread in the glass rod according to the numerical aperture of the optical fiber, and the laser light is output from a second endface of the glass rod. Thus, spreading the diameter of laser light allows for reduction in power intensity of laser light at the output end of the glass rod (Patent Document 1).